Technical Field
The present invention relates to a drilling fluid composition that contains micronized barite particles as a weighting agent, and also a method of fracturing a subterranean formation using the drilling fluid composition.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Drilling fluids or muds are used in the rotary drilling process of wells to tap underground collections of oil and gas. These muds have several functions. The most important functions are to assist in the removal of cuttings from the well, to seal off unwanted formations which may be encountered at different levels preventing the loss of drilling fluids to void spaces and to permeable or porous formations, to lubricate the drilling tool, to maintain the well bore pressure and stability of the bore hole, and to hold the cuttings in the suspension during events of shutdowns in drilling.
Drilling fluid additives form a thin, low permeability filter cake (mud cake) over time that seals openings in formations to reduce the unwanted influx of fluids into permeable formations. A mud cake forms when the drilling fluid contains particles that are approximately the same size as or have diameters greater than about one third of the pore diameter (or the width of any opening such as induced fractures) in the formation being drilled. The drilling fluid must circulate in the wellbore (down the drill pipe and back up the annulus) to perform the above mentioned functions for the drilling process to continue smoothly. Therefore, the drilling fluid must remain in the wellbore all the time in order to control and prevent caving of the wellbore.
Drilling fluid compositions generally include one or more weighting agents such as barite, iron oxides, manganese tetraoxide, potassium formate, hematite, and calcium carbonate, etc. to increase the overall density of the drilling fluid so that sufficient bottom hole pressure can be maintained thereby preventing an unwanted influx of formation fluids.
Barite is one of the most common weighting agents used in drilling fluids, completion fluids, cementing fluids, etc. in deep oil and gas wells. Generally, the barite particle size used in drilling fluid ranges from 30 to 70 μm. The invasion of the mud filtrate due to the pressure difference will create mud cake that mainly composed of barite having particle size of 30 to 70 μm, which can cause barite scale formation and further reduce the reservoir permeability. Additionally, it was shown that barite particles facilitate the formation of barite scales around casing and production tubing, yet cause erosion of surface chokes and valves. Consequently, the process of removing the mud cake (filter cake) and/or barite scales could be very costly, particularly in horizontal reservoirs and extended reach wells, when barite particles with a particle size of 30 to 70 μm is used as the weighting agent in the formulation of the drilling fluid.
In view of the forgoing, one objective of the present invention is to provide a drilling fluid composition that contains micronized barite particles as a weighting agent, and to provide a method of fracturing a subterranean formation using the drilling fluid composition.